I don't think that's the reason, because in previous stock version the SDCard in exFAT works just fine for me. But thank you for your effort! I'll keep an eye on this thread.
I can confirm this after reformatting my sdcard twice, once with Windows8/FAT32 and with the phone itself (settings/storage/erase).
Hopefully this is the last big hurdle to a close to perfect vanilla ROM. Wait for devvers (Cyanogen?) to solve this.